Electro-magnetic cut-out



(No Model.) '2 Sheets-Sheet 1. S. H. COBB.

ELECTED MAGNETIC GUT-OUT. No. 456,940. Patented Aug. 4, 1891.

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(No Model.) 2 Sheets-Sheet 2.

I s. H. COBB.

ELEGTRO MAGNETIC GUT-OUT.

No. 456,940. Patented Aug. 4, 1891.

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SYLVANUS H. COBB, OF HYDE PARK, MASSACHUSETTS, ASSIGNOR TO THEELECTRICAL SAFETY COMPANY, OF PORTLAND, MAINE.

ELECTRO-MAGNETIC CUT-OUT.

SPECIFICATION forming part of Letters Patent No. 456,940, dated August4, 1891.

Application filed November 29, 1890. Serial No. 373,023. (No modeld Toall whom it may concern.- I

Be it known that I, SYLVANUS H. COBB, of Hyde Park, in the county ofNorfolk and State of Massachusetts, have invented a new and usefulImprovement in Current-Protectors for Electrical Instruments, of whichthe follow 111g, taken in connection with the accompa- Y nying drawings,is a specification.

This invention relates to that class of protectors for electricalinstruments in which class a current above the strength which can bereceived without injury by the instrument to be protectedisautomaticallydiverted from the instrument as long as the current remainsat this strength, but in which the circuit through the instrument to beprotected is automatically reestablished when the current falls to thatstrength which will not injure the protected instrument, thus leavingthe instrument in circuit.

The object of this invention is to obtain a protector which will becapable of being operated by currents of feeble strength-as, forexample, What is known as sneak currents and which will also receivewithout 1n3ury much stronger currents, thus increasing the efficiency ofthe instrument by enlarging thelimits of current strength within whichit will be operative.

In protecting instruments of the class referred to a contact-pointthrough which the circuit is directed is attached to the armature of anelectro-magnet included in the circuit, and when this electro-magnet isenergized the armature is attracted, and the contact-point attachedthereto is caused to establ sh a connection with the ground, and thecircuit through the protected instrument is broken. The sensitiveness ofthe clectro-magnet to currents passing through its helix isproportional, other factors being equal, to the number of turns in thishelix; but as each turn adds to the resistance of the helix it isobvious that increase in sensitiveness is accompanied by increasedresistance, and con-' would be useful for protecting against weakcurrents would therefore be useless as a protector for strong currents,and would, in fact, be a source of danger, owing to the heat produced bythe resistance of its helix to the strong current.

In the application of protecting devices to electrical instruments it iscustomary to include in the circuit apiece of wire of high resistanceknown asa safety-fuse, which wire is burned out by a strong currententering the line. 'Ihedestruction of this wire necessarily breaks thecircuit, a result which it is desirable to avoid, especially when theprotector is applied to fire-alarm instrumentsa class of instrumentswhich are of little value unless at all times available for use. p

In the invention which forms the subject of this application for LettersPatent of the United States there is a wide range of current strengthbetween which the instrument will operate, and consequently the safety-fuse will only be required as a protection against currents of verygreatstrength, and there will. be but little possibility, under theconditions which ordinarily prevail upon lines, of the circuit becomingbroken.

I have shown my invention in connection with the protector described inand claimed in Letters Patent of the United States No. 820,912, issuedto David J. Cartwright June 30, 1885; but it is obvious that theprinciple of my invention can be carried into efiect with any protectingdevice in which an electro-magnet acts to divert the dangerous currentfrom the instrument to be protected.

For the purpose of accomplishing the desired object the inventionconsistsin the com= bination, substantially as and for the purposehereinafter more fully set forth, with the electro-magnet, of aresistance connected with the line and of two armatures, one of which isattracted by currents of feeble strength and causes the diversion of thecurrent from the instrument to be protected, and the other which isattracted by strong currents, and which when attracted causes a divisionof the current between the electro-niagnet and the resistance to such anextent that injury to the magnet by heating is prevented.

In the accompanyingdrawings, Figure 1 is a front View of my device. Fig.2 is a side view in elevation of the same. Fig. 3 is an end view of thesame, and Fig. at is a diagram showing the electrical connections.

In the several figures the same letters refer to the same parts.

' The peculiarity of the Cartwright protector is that the current iscarried to the ground through the core of the electro-magnet.

Referring to the drawings, A is a suitable base-board which supports theparts of the instrument.

B is the electro-magnet.

C is a standard of metal attached to the base-board, and D is anarmature attached to one end of a lever E, pivoted to this standard. Theother arm of the lever carries an adjustable weight a and balances thearmature, the position of this weight determiningthe sensitiveness ofthe armature to the current pass ing through the electro-magnet B.

The instrument to be protected is electrically connected to the standardC by the binding-screw F, and from this screw a wire 1) passes to oneend of the helix on the electromagnet. The other end of this helix isconnected by a Wire 0 with a binding-screw G on the metallic plate H,attached to the baseboard, and this binding-screw is connected to theline.

Opposite the other end of the magnet B is another metallic standard I,to which is pivoted the lever K, one arm of which carries the armature Land the other arm the adjustable Weight M. This armature is heavier thanthe armature D, and is not attracted under the action of the feeblecurrents which cause the attraction of the armature D.

N is a metallic plate which is metallically connected to the core of themagnet, and on the plate is a binding-post P, which is connected to theground.

Between the standard I and the metallic plate H is interposed aresistance 0, preferably a rod of hard carbon, and which should be ofless resistance than the helix on the electro-magnet. Carbon blocks (1may be placed upon the poles of the armature L and on the extremity ofthe core of the magnet for the purpose of preventing the adhesion of thearmature of the core by fusing in case that the current through the coreshould be Very strong. Carbon blocks may also be placed upon the face ofthe other armature D and upon the end of the core opposite to thisarmature for the same purpose.

The requirements of the telephone service demand that the instrumentsshould not be exposed to currents greater than three-tenths of anampere, and the armature D is therefore so adjusted and the magnet B isof such dimensions and so wound that a current of this strength, or, ifdesired, of feebler strength,

wire C, helix of the magnet, wire 1), binding screw F, to the instrumentto be protected; but when for any reason'as, for example, accidentalcontact of the line-wire with a wire carrying a sneak current for anelectric light or power wire-the current on the line becomessufliciently strong to attract the armature D, the armature is drawn incontact with the core and the current is diverted from the instrument tobe protected and passes through the standard C and armature D and thecore of the magnet, and thence to the ground through the binding-post N.\Vhen a strong current comes on the line, and one which may be ofsuiiicient strength to unduly heat the helix of the electro-magnet B,the armature L is attracted and the standard I is electrically connectedto the core and the metallic plate l attached thereto and thus to theground, so that a path is afforded for the current through the carbonrod 0. Currents divide between two or more branch circuits in proportionto the resistance of these branches, and therefore sufficient currentwill pass through the helix to maintain the armatu res in contact withthe core, but not enough current to heat the helix sufficiently toinjure it, for the reason that a large part of the current will passthrough rod 0. As this carbon rod becomes heated by the passage of thecurrent its resistance diminishes, and consequently the stronger thecurrent the greater the proportionate part which will pass through thecarbon rod, and for this reason undue heating of the helix by a strongcurrent cannot take place.

In the instrument represented in. the accompanying drawings as embodyingthe principle of my invention the electro-magnet is represented as in avertical position and the retraction of the armature is obtained bymeans of the adjustable Weights on the levers, to which armatures areattached; but the magnet may be placed horizontally and the retractingforce may be obtained by means of springs.

Having thus described my in vention, what I claim, and desire to secureby Letters Patent of the United States, is

1. In a currentprotector for electrical instruments, the combination,substantially as and for the purpose set forth, of an electromagnetincluded in the circuit and acting by the movement of its armature whenthe magnet is energized by a current of strength sufficient to injurethe instrument to be protected to establish a connection with ground, aresistance less than the resistance of the magnet and connected to thecircuit, a supplementary armature electrically connected to thisresistance, operated by the same or another electro-magnet in thecircuit and not attracted except by currents stronger than those whichcause the attraction of the other armature, and connections, asdescribed, whereby the attraction of the supplementary armatureestablishes the connection of the resistance with the electro magnet ormagnets and ground, thus causing a division of the current between thisresistance and the electro magnet or magnets.

2. In a current-protector for electrical instruments, the combination,substantially as and for the purpose set forth, of an electromagnetincluded in the circuit and having its core electrically connected toground, an adj ustable armature adjusted to be attracted as soon as thecurrent becomes strong enough to injure the instrument to be protected,and when attracted establishing a path for the current to the groundthrough the core of the magnet, a resistance less than the resistance ofthe magnet and connected to the circuit, and a supplementary adjustablearmature for the elect-ro-magnet so adjusted and of such size that it isnot attracted by the currents which cause the attraction of the othermagnets, but only by stronger currents, and electrically connected tothe resistance, whereby when the supplementary magnet is attracted tothe core the strong current is divided between the resistance and theelectro-inagnet, and injurious heating of the magnet is prevented.

3. In a current-protector for electrical instruments, the combination,substantially as and for the purpose set forth, of the base- 0 board A,the vertical electro-magnet B, supported upon this base-board, themetallic standard N, connected to the core of the magnet and to theground, the metallic standard 0, connected to the instrument to beprotected, the metallic lever E, pivoted on this standard and carryingon one arm an armature E and 011 the other an adjustable weight, themetallic plate H, connected to the line, the carbon rod 0, attached tothis plate, the metallic standard I, metallically connected to the otherend of this rod, and the metallic lever pivoted to this standard andcarrying on one arm an adjustable weight M and on the other the armatureL, of such weight and adjustment that it is not attracted by thecurrents which attract the armature D, but only by stronger currents,and the wires 1) 0, connected with the terminals of the helix to thebindingposts F and G, respectively.

In testimony whereof I have signed my name to this specification, in thepresence of two subscribing Witnesses, on this 26th day of November, A.D. 1890.

SYLVANUS H. COBB.

\Vitnesses:

JOHN H. CooMBs, HENRY S. BUNTON.

